The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, a hard disk drive (HDD) 10 includes a hard disk assembly (HDA) 12 and a HDD printed circuit board (PCB) 14. The HDA 12 includes one or more circular platters 16, which have magnetic surfaces that are used to store data magnetically. Data is stored in binary form as a magnetic field of either positive or negative polarity. The platters 16 are arranged in a stack, and the stack is rotated by a spindle motor 18. At least one read/write head (hereinafter, “head”) 20 reads data from and writes data on the magnetic surfaces of the platters 16.
Each head 20 includes a write element, such as an inductor, that generates a magnetic field and a read element, such as a magneto-resistive (MR) element, that senses the magnetic field on the platter 16. The head 20 is mounted at a distal end of an actuator arm 22. An actuator, such as a voice coil motor (VCM) 24, moves the actuator arm 22 relative to the platters 16.
The HDA 12 includes a preamplifier device 26 that amplifies signals received from and sent to the head 20. When writing data, the preamplifier device 26 generates a write current that flows through the write element of the head 20. The write current is switched to produce a positive or negative magnetic field on the magnetic surfaces of the platters 16. When reading data, the magnetic fields stored on the magnetic surfaces of the platters 16 induce low-level analog signals in the read element of the head 20. The preamplifier device 26 amplifies the low-level analog signals and outputs amplified analog signals to a read/write channel (hereinafter, “read-channel”) module 28.
The HDD PCB 14 includes the read-channel module 28, a hard disk controller (HDC) module 30, a processor 32, a spindle/VCM driver module 34, volatile memory 36, nonvolatile memory 38, and an input/output (I/O) interface 40. During write operations, the read-channel module 28 may encode the data to increase reliability by using error-correcting codes (ECC) such as run length limited (RLL) code, Reed-Solomon code, etc. The read-channel module 28 then transmits the encoded data to the preamplifier device 26. During read operations, the read-channel module 28 receives analog signals from the preamplifier device 26. The read-channel module 28 converts the analog signals into digital signals, which are decoded to recover the original data.
The HDC module 30 controls operation of the HDD 10. For example, the HDC module 30 generates commands that control the speed of the spindle motor 18 and the movement of the actuator arm 22. The spindle/VCM driver module 34 implements the commands and generates control signals that control the speed of the spindle motor 18 and the positioning of the actuator arm 22. Additionally, the HDC module 30 communicates with an external device (not shown), such as a host adapter within a host device, via the I/O interface 40. The HDC module 30 may receive data to be stored from the external device, and may transmit retrieved data to the external device.
The processor 32 processes data, including encoding, decoding, filtering, and/or formatting. Additionally, the processor 32 processes servo or positioning information to position the heads 20 over the platters 16 during read/write operations. Servo, which is stored on the platters 16, ensures that data is written to and read from correct locations on the platters 16. In some implementations, a self-servo write (SSW) module 42 may write servo on the platters 16 using the heads 20 prior to storing data on the HDD 10.
Timing recovery in the read-channel module 28 begins with zero phase start (ZPS). ZPS includes calculating phase information. The phase information enables timing recovery to begin data-acquisition with minimum phase-error.
Referring now to FIG. 2, the read-channel module 28 may comprise an input module 52, a variable-gain amplifier (VGA) module 54, a filter module 56, an analog-to-digital converter (ADC) module 58, a zero phase start (ZPS) module 60, a timing recovery module 62, and an automatic gain control (AGC) module 64.
The input module 52 receives read signals generated by heads 20. The VGA module 54 amplifies the read signals. The filter module 56 filters the amplified read signals. The ADC module 58 converts the amplified and filtered read signals from analog to digital format and generates samples.
The ZPS module 60 calculates phase information from the samples. Based on the phase information, the timing recovery module 62 determines when the phase error in the samples is minimum. That is, the timing recovery module 62 determines the time at which data may be correctly recovered from the -output of the ADC module 58 with minimum phase-error.
Additionally, the ZPS module 60 controls the gain of the AGC module 64. The AGC module 64, in turn, controls the gain of the VGA module 54. The gain of the VGA module 54 determines the amplitude of the output of the ADC module 58. For example, if the gain of the VGA module 54 is very high, the output of the ADC module 58 may be saturated. In that case, the ZPS module 60 may generate incorrect phase information. On the other hand, if the gain of the VGA module 54 is very low, the output of the ADC module 58 may be very low, and the ZPS module 60 may be unable to detect phase information.
In either case, the timing recovery module 62 may be unable to determine the time at which data may be correctly recovered from the output of the ADC module 58 with minimum phase-error. Consequently, data may be recovered from the output of the ADC module 58 at incorrect times, and the data thus recovered may be incorrect.